Conventionally, a mold for resin molding in which an uneven mold surface for forming an uneven pattern is formed on a resin layer bonded to a base material and whiskers having a length of 10 to 300 μm are mixed in the resin layer has been known as an example of a mold for resin molding for manufacturing a resin molded article having an uneven pattern on a surface thereof (e.g. patent literature 1). In this mold for resin molding, the resin layer is neither deformed nor altered by heat or external force and a fine uneven pattern can be formed on a surface of a resin molded article, and a reduction in weld lines at the time of molding brought about by a heat insulation effect of the resin layer is also expected.
However, in the case of using in a vacuum molding tool for which exhaust holes need to be secured, this mold for resin molding cannot be used as the vacuum molding tool as it is since the exhaust holes are concealed by providing the surface-textured resin layer on the mold. To secure the exhaust holes formed in the mold, it is thought to perforate holes at the same positions as the exhaust holes (hereinafter, referred to as a hole forming operation) in this case by forming holes in the resin layer by wire materials inserted through the exhaust holes from the underside of the mold after the surface-textured resin layer is provided on the mold surface. However, since the vacuum molding tool has many exhaust holes, substantial effort is required for the hole forming operation. In addition, there may arise a problem that the exhaust holes are clogged at the time of vacuum molding. In such a case, it is essential to clean the holes, which also requires substantial effort.
Accordingly, it has been proposed a mold for resin molding which has air permeability without requiring substantial effort. That is, this mold for resin molding includes a molding tool, a design layer formed on an inner side of the molding tool and an air-permeable intermediate layer used to provide the design layer on an inner side surface of the molding tool. The molding tool is formed with through holes for ventilation, the design layer is formed of a resin having an uneven shape on its surface, and through holes for ventilation are perforated to communicate with the through holes for ventilation, and the air-permeable intermediate layer is continuously provided on the inner side surface of the molding tool so that an inner side surface of the design layer, the through holes for ventilation of the design layer and the through holes for ventilation of the molding tool communicate with each other (see, for example, patent literature 2).
In this mold for resin molding, exhaust holes can be easily provided at desired positions without perforating the surface-textured layer made of the resin with exhaust holes communicating with exhaust holes provided in the vacuum mold in advance. In this mold for resin molding, the exhaust holes can be easily perforated by bonding and fixing the surface-textured layer made of the resin to the mold via the “air-permeable intermediate layer” instead of directly bonding and fixing it to the mold.
That is, since the air-permeable intermediate layer is provided in this mold for resin molding, it is possible to eliminate the need for forming holes at the same positions as the through holes for ventilation, i.e. exhaust holes provided in the mold in advance and relatively easily form the through holes for ventilation, i.e. holes for exhaust. Thus, in the hole forming operation of forming the through holes for ventilation that is performed after the design layer is provided, the holes can be formed at arbitrary positions as long as they have a depth to reach the air-permeable intermediate layer. Therefore, if the through holes for ventilation are clogged during molding, holes can be easily formed at other positions even if the holes are not cleaned.